全文获取类型
收费全文 | 35196篇 |
免费 | 3860篇 |
国内免费 | 2163篇 |
专业分类
电工技术 | 2313篇 |
技术理论 | 1篇 |
综合类 | 3309篇 |
化学工业 | 5271篇 |
金属工艺 | 965篇 |
机械仪表 | 2116篇 |
建筑科学 | 2160篇 |
矿业工程 | 652篇 |
能源动力 | 1228篇 |
轻工业 | 2162篇 |
水利工程 | 519篇 |
石油天然气 | 898篇 |
武器工业 | 463篇 |
无线电 | 3703篇 |
一般工业技术 | 4999篇 |
冶金工业 | 1396篇 |
原子能技术 | 333篇 |
自动化技术 | 8731篇 |
出版年
2024年 | 201篇 |
2023年 | 594篇 |
2022年 | 922篇 |
2021年 | 1054篇 |
2020年 | 1275篇 |
2019年 | 1118篇 |
2018年 | 1049篇 |
2017年 | 1314篇 |
2016年 | 1443篇 |
2015年 | 1467篇 |
2014年 | 2128篇 |
2013年 | 2318篇 |
2012年 | 2544篇 |
2011年 | 2890篇 |
2010年 | 2098篇 |
2009年 | 2175篇 |
2008年 | 1838篇 |
2007年 | 2167篇 |
2006年 | 1897篇 |
2005年 | 1527篇 |
2004年 | 1295篇 |
2003年 | 1189篇 |
2002年 | 984篇 |
2001年 | 774篇 |
2000年 | 690篇 |
1999年 | 595篇 |
1998年 | 524篇 |
1997年 | 453篇 |
1996年 | 365篇 |
1995年 | 339篇 |
1994年 | 293篇 |
1993年 | 221篇 |
1992年 | 185篇 |
1991年 | 157篇 |
1990年 | 134篇 |
1989年 | 126篇 |
1988年 | 110篇 |
1987年 | 81篇 |
1986年 | 68篇 |
1985年 | 81篇 |
1984年 | 97篇 |
1983年 | 108篇 |
1982年 | 111篇 |
1981年 | 47篇 |
1980年 | 37篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1959年 | 5篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Laura M. Haas Michael J. Carey Miron Livny Amit Shukla 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(3):241-256
In this paper, we re-examine the results of prior work on methods for computing ad hoc joins. We develop a detailed cost model for predicting join algorithm performance, and we use the model to develop cost formulas
for the major ad hoc join methods found in the relational database literature. We show that various pieces of “common wisdom” about join algorithm
performance fail to hold up when analyzed carefully, and we use our detailed cost model to derive op
timal buffer allocation schemes for each of the join methods examined here. We show that optimizing their buffer allocations
can lead to large performance improvements, e.g., as much as a 400% improvement in some cases. We also validate our cost model's
predictions by measuring an actual implementation of each join algorithm considered. The results of this work should be directly
useful to implementors of relational query optimizers and query processing systems.
Edited by M. Adiba. Received May 1993 / Accepted April 1996 相似文献
92.
根据克拉贝龙—克劳修斯方程,建立了国内外文献未见报道的测定导热油热分解温度的试验装置和试验方法,测定了大量国内外导热油的热分解温度,数据表明该法具有准确、简单、实用、省时、省力等优点 相似文献
93.
Gong-Liang Li Ishihara Tatsumi Moro-oka Yoshihiko Takita Yusaku 《Applied catalysis. B, Environmental》1996,9(1-4):239-249
The catalytic decomposition of CHClF2 was studied over various acidic metal oxides in a fixed-bed reactor. The Cr2O3ZrO2 exhibited the highest activity. The presence of water vapor in the reaction system suppresses the transformation of oxides to fluorides, progresses the formation of CO2, and it improves the catalysts life. 相似文献
94.
关于彩色火焰蜡烛的研制 总被引:1,自引:0,他引:1
本文阐述了利用焰色反应的原理研制彩色火焰蜡烛,着重分析并解决了在研制工作中出现的几个技术关键,如主燃剂的选取、蜡烛成型和强度、发色剂的选择与用量等. 相似文献
95.
96.
寻找非构造油气藏的新思路 总被引:3,自引:0,他引:3
目前,一种新的理论体系和研究方法已经形成,并正在发展和逐步完善。那就是层序地层学和油气成藏系统理论的诞生和发展;以及由计算机的快速发展带动起来的地震测井资料的采集、处理、显示和各种地质问题的计算机模拟技术,使得地质学和石油地质学都在朝着从定性到定量,从推测到更科学的预测方向发展。在今后的5~10年中,中国的石油地质家们不仅要注意方法和技术方面的进步,还应当重视在陆相层序地层学和陆相层序中油气成藏机制等基本理论方面的研究。 相似文献
97.
The MSMIE protocol [SBC89] allows processors in a distributed system to communicate via shared memory. It was designed to meet the reliability and efficiency needs of applications such as nuclear safety systems. We present a formal model of the MSMIE protocol expressed in the notation CCS. Desirable properties of the protocol are expressed in the modal mu-calculus, an expressive modal logic. We show that the protocol lacks an important liveness property. In actual operation, additional operating constraints are checked to avoid potential problems. We present a modified protocol and show that it possesses the liveness property even without checking operating constraints. We also show how parts of the analysis were automated with the Concurrency Workbench. 相似文献
98.
99.
Jiang Taihui 《电子科学学刊(英文版)》1996,13(4):325-332
In this paper, an adaptive line spectral pair filter is derived from an adaptive lattice filter. A least-mean-square(LMS) type adaptive algorithm used to calculate directly the line spectral pair(LSP) coefficients on a stage-by-stage basis is presented. Experimental results show that the algorithm has higher convergence rate and lower misadjustment as compared with the other algorithms. The LSP coefficients calculated by the algorithm have been used to carry out speech linear predictive synthesis, resulting in better results than PARCOR coefficients. 相似文献
100.
Annual commercial poplar wood production in Turkey is about 3.6 million cubic meters, half of which comes from hybrid poplar I-214. The poplar plantation areas of Turkey are 70% of the poplar plantation areas of the Near and Middle Eastern countries, and nearly 5% of the world. In this study, unit times of standard operations were investigated in poplar nurseries and plantations in which new mechanical technology was applied and compared with traditional methods. Analyses of unit times were made on 11 treatments for poplar nurseries and nine treatments for poplar plantations; some new methods are also recommended. Mechanization methods based on new technologies give promising results in poplar nurseries and plantations. 相似文献